Inbreeding...what's the deal?

A friend of a friend was working in a hotel in Dubai (Arab Emerites), one of the super-rich ones that cater to royalty. She said that most of the royals looked peculiar, had asymmetrical faces, funny eyes, strange temperments (i.e. nutzo) etc... and was speculating that this was the result of inbreeding, which is quite frequent amongst the royal families for monetary reasons. This was also the case with many European royals in decades past. I'm sure some of the weird behaviour could be attributed to them being richer than God and having nothing else to do all day but be insane, but the physical changes are harder to explain away.

So my question is: why does inbreeding cause an increase in the number of mental/physical defects? Does anyone who studied biology have a simple explanation? Kissing your sister might make you disgusting, but how does it make your kids crazy?

Originally posted by PBE6
A friend of a friend was working in a hotel in Dubai (Arab Emerites), one of the super-rich ones that cater to royalty. She said that most of the royals looked peculiar, had asymmetrical faces, funny eyes, strange temperments (i.e. nutzo) etc... and was speculating that this was the result of inbreeding, which is quite frequent amongst the royal families for m lanation? Kissing your sister might make you disgusting, but how does it make your kids crazy?

I would be crazy if I found out that my father was having sex with his sister...😠

I'm not sure, but I will take an educated guess.

Obviously, many of us are carriers of some form of genetic mutation, even if we do not show it. In other words, the mutated gene might be recessive (hopefully you understand that, otherwise this will be difficult to explain). So, if two close relatives have similar problematic genes, the probability of their offspring having mutations will increase. Again, I'm no doctor or scientist, but it's my best guess.

Originally posted by wittywonka
I'm not sure, but I will take an educated guess.

Obviously, many of us are carriers of some form of genetic mutation, even if we do not show it. In other words, the mutated gene might be recessive (hopefully you understand that, otherwise this will be difficult to explain). So, if two close relatives have similar problematic genes, the probability of ...[text shortened]... g having mutations will increase. Again, I'm no doctor or scientist, but it's my best guess.

I agree that the number of recessive traits expressed would increase with the number of identical recessive genes possessed by the group, but are all recessive traits bad? I don't think so. Isn't blue eyes a recessive trait?

Originally posted by PBE6
I agree that the number of recessive traits expressed would increase with the number of identical recessive genes possessed by the group, but are all recessive traits bad? I don't think so. Isn't blue eyes a recessive trait?

True, but a lot are bad and these are what matter.

Originally posted by Bad wolf
True, but a lot are bad and these are what matter.

Is there any evidence for this though? According to Wikipedia (http://en.wikipedia.org/wiki/Inbreeding), cheetahs have problems with viruses (which none of them have immunity to because of inbreeding), but not with genetic disorders:

"The cheetah once was reduced by disease, habitat restriction, overhunting of prey, competition from other predators (primarily lions, competition from human land use, etc.) to a very small number of individuals.[1][2] All cheetahs now come from this very small gene pool. Should a virus appear that none of the cheetahs have resistance to, extinction is always a possibility. Currently, the threatening virus is feline infectious peritonitis, which has a disease rate in domestic cats from 1%-5%; in the cheetah population it is ranging between 50% to 60%. The cheetah is also known, in spite of its small gene pool, for few genetic illnesses."

It also mentions the heartiness of inbred island animal populations:

"Island species are often very inbred, as their isolation from the larger group on a mainland allows for natural selection to work upon their population. This type of isolation may result in the formation of race or even speciation, as the inbreeding first removes many deleterious genes, and allows expression of genes that allow a population to adapt to an ecosystem. As the adaptation becomes more pronounced the new species or race radiates from its entrance into the new space, or dies out if it cannot adapt and, most importantly reproduce.[3]"

Originally posted by PBE6
Is there any evidence for this though? According to Wikipedia (http://en.wikipedia.org/wiki/Inbreeding), cheetahs have problems with viruses (which none of them have immunity to because of inbreeding), but not with genetic disorders:

"The cheetah once was reduced by disease, habitat restriction, overhunting of prey, competition from other predators (primari ...[text shortened]... ance into the new space, or dies out if it cannot adapt and, most importantly reproduce.[3]"

It's not a matter of recessive genes, the problem is caused by genes whose expression is bad for the organism carrying it. If a gene is dominant then it will be expressed and if it causes sufficiently bad problems for the organism then it will only last a generation. I think that this is what is happening in Island species. Because of the small population you get bad genes being expressed more quickly and killed off by natural selection - or the species goes extinct on the island.

Also it depends on what you mean by a bad gene. The sickle cell anemia gene is a problem if you have both - you have a life expectancy of about 40 and are liable to get attacks slightly less than once a year. If you have one you have a higher resistance to malaria. So the gene is good if you live in a malarial area.

Originally posted by PBE6
Is there any evidence for this though? According to Wikipedia (http://en.wikipedia.org/wiki/Inbreeding), cheetahs have problems with viruses (which none of them have immunity to because of inbreeding), but not with genetic disorders:

"The cheetah once was reduced by disease, habitat restriction, overhunting of prey, competition from other predators (primari ...[text shortened]... ance into the new space, or dies out if it cannot adapt and, most importantly reproduce.[3]"

How does inbreeding remove deleterious genes? Wouldn't inbreeding in humans increase chances of inheriting a deleterious recessive gene from a common ancestor?

Originally posted by HandyAndy
How does inbreeding [b]remove deleterious genes? Wouldn't inbreeding in humans increase chances of inheriting a deleterious recessive gene from a common ancestor?[/b]

yes.

When I was younger I thought my second cousin was hot. In fact, I still do, she is gorgeous.

But isn't this the reason you have to get blood tests before marriage, to make sure you are not about to marry a relative and have messed up kids?

Originally posted by PocketKings
you have to get blood tests before marriage

You do?

As far as my biological input goes:

When non-relatives reproduce, the kids will have DNA from both parents. Random mutations make them unique. Any flaws in the DNA of one parent are "fixed" by the corresponding DNA frmo the other parent.

With inbreeding there is not sufficient "fresh" DNA in the mixture to compensate all flaws. Generation upon generation the flaws will become bigger and bigger, until the newborns will not survive anymore.

These changes do take a couple of generations, so a child of a man and his sister is most likely 'normal' .

Originally posted by PocketKings
yes.

When I was younger I thought my second cousin was hot. In fact, I still do, she is gorgeous.

But isn't this the reason you have to get blood tests before marriage, to make sure you are not about to marry a relative and have messed up kids?

No. Premarital blood tests, in the states that still require them, are for sexually transmitted diseases, not genetic links.

Originally posted by TheMaster37
You do?

As far as my biological input goes:

When non-relatives reproduce, the kids will have DNA from both parents. Random mutations make them unique. Any flaws in the DNA of one parent are "fixed" by the corresponding DNA frmo the other parent.

With inbreeding there is not sufficient "fresh" DNA in the mixture to compensate all flaws. Generatio ...[text shortened]... take a couple of generations, so a child of a man and his sister is most likely 'normal' .

This can't be true. The cheetah example reported above is a sound counter-argument. Besides, what makes "fresh" DNA better than "same old" DNA? Here's the answer: fresh injections of DNA into the gene pool leads to genetic diversity, which will enable a group of organisms adapt to their environment much more readily than the "all the eggs in one basket" approach you get by copying the same old DNA every time. However, this does not explain the problems normally attributed to inbreeding.

Also, if introducing a random mutation into a perfectly harmonized set of genes were so deleterious, you would expect disastrous results from introducing a whole pile of non-standard genes into the same set - but this is exactly the opposite of what is observed.

Originally posted by PBE6
Also, if introducing a random mutation into a perfectly harmonized set of genes were so deleterious, you would expect disastrous results from introducing a whole pile of non-standard genes into the same set - but this is exactly the opposite of what is observed.

Maybe, but it isn't a random collection of genes that you're introducing, is it? It's a collection of genes that have already proven they are effective in lots of different combinations.

Originally posted by mtthw
Maybe, but it isn't a random collection of genes that you're introducing, is it? It's a collection of genes that have already proven they are effective in lots of different combinations.

That's inconsequential. What's the difference between genes from a distantly related organism that have proven themselves effective, and genes from a closely related organism that have also proven themselves effective? They are both effective gene sets.

Originally posted by DeepThought
It's not a matter of recessive genes, the problem is caused by genes whose expression is bad for the organism carrying it. If a gene is dominant then it will be expressed and if it causes sufficiently bad problems for the organism then it will only last a generation. I think that this is what is happening in Island species. Because of the small popula ...[text shortened]... d more quickly and killed off by natural selection - or the species goes extinct on the island.

I agree. There may be some short-term detriment to some of the organisms who express the deleterious recessive traits (i.e. death, or inability to pass on genetic material to descendants), but overall the group will eventually be purged of these deleterious traits to a workable degree provided the group has indeed survived.

So why does inbreeding appear to lead down a road to destruction? Is it just a problem with the time scale we're viewing it in? Will it eventually lead to more robust organisms? Does it even really lead to ruin in the short term, more often than interbreeding does? Animal populations, especially those controlled closely by humans (like dogs, cats, pigs, cattle, etc...) are often subject to extreme inbreeding, but they seem just fine.